Eukaryotic hexosamine biosynthesis and GlcNAc salvage

A reusable eukaryotic pathway that converts fructose 6-phosphate to UDP-N-acetylglucosamine through glutamine-dependent amination, acetyl-CoA- dependent N-acetylation, phosphomutase conversion, and UTP-dependent uridylyl transfer, all catalysed by soluble cytosolic enzymes. The eukaryotic order (N-acetylation of glucosamine 6-phosphate before the 6-phosphate to 1-phosphate mutase step) differs from the bacterial route, in which glucosamine 6-phosphate is first isomerised to the 1-phosphate and then acetylated and uridylylated by a bifunctional enzyme. In animals and some other eukaryotes a GlcNAc-kinase salvage branch enters at the N-acetylglucosamine 6-phosphate intermediate. Feedback inhibition of the first, glutamine-dependent amidotransferase by UDP-GlcNAc couples pathway flux to nutrient availability and glycosylation demand. The product supplies protein N-glycosylation, GPI-anchor synthesis, chitin synthesis in fungi, proteoglycan synthesis and O-GlcNAcylation in animals, and the sialic-acid route.

MODULE:hexosamine_biosynthesisDRAFTCONCRETEMetabolic Pathwaymodules/hexosamine_biosynthesis.yaml
UDP-N-acetylglucosamine biosynthetic processGO:0006048
YeastPathways:UDPNAGSYN-YEAST-PWY
UDP-N-acetylglucosamine biosynthesis (S. cerevisiae, SGD YeastPathways)
YeastCyc lists L-GLN-FRUCT-6-P-AMINOTRANS-RXN (GFA1), GLUCOSAMINEPNACETYLTRANS-RXN (GNA1), PHOSACETYLGLUCOSAMINEMUT-RXN (PCM1) and NAG1P-URIDYLTRANS-RXN (QRI1). All four gene assignments were retained; no salvage kinase is listed for S. cerevisiae.
GO:0006048
UDP-N-acetylglucosamine biosynthetic process
The four de novo steps carry out UDP-GlcNAc biosynthesis (GO:0006048).
GO:0006047
UDP-N-acetylglucosamine metabolic process
NAGK salvages free GlcNAc into the UDP-GlcNAc metabolic pathway (GO:0006047).
PMID:16408321
Enzymes of UDP-GlcNAc biosynthesis in yeast.
Review of the four-step cytoplasmic UDP-GlcNAc pathway in Saccharomyces cerevisiae and Candida albicans.
The glucosamine-containing sugar nucleotide UDP-GlcNAc is synthesized in yeast cells in a four-step cytoplasmic pathway.
PMID:2656689
Cloning of the glutamine:fructose-6-phosphate amidotransferase gene from yeast. Pheromonal regulation of its transcription.
GFA1 encodes the yeast L-glutamine:D-fructose-6-phosphate amidotransferase.
PMID:9867860
Saccharomyces cerevisiae GNA1, an essential gene encoding a novel acetyltransferase involved in UDP-N-acetylglucosamine synthesis.
GNA1 encodes glucosamine-6-phosphate acetyltransferase; with Agm1p (PCM1) and Uap1p (QRI1) it converts glucosamine 6-phosphate to UDP-GlcNAc, and the yeast acetyltransferase and pyrophosphorylase are separate essential genes rather than the fused bacterial GlmU.
These results indicate that YFL017C specifies glucosamine-6-phosphate acetyltransferase; therefore, the gene was designated GNA1 (glucosamine-6-phosphate acetyltransferase).
PMID:8174553
Characterization of the essential yeast gene encoding N-acetylglucosamine-phosphate mutase.
AGM1 (PCM1) is the essential structural gene for N-acetylglucosamine-phosphate mutase.
PMID:9603950
The eukaryotic UDP-N-acetylglucosamine pyrophosphorylases. Gene cloning, protein expression, and catalytic mechanism.
Yeast UAP1 (QRI1), Candida albicans and human UAP1 encode UDP-GlcNAc pyrophosphorylase; the mutase reaction precedes uridyl transfer in eukaryotes.
These results demonstrate that the UAP1 genes indeed specify eukaryotic UDP-GlcNAc pyrophosphorylase and that phosphomutase reaction precedes uridyltransfer.
file:human/GFPT1/GFPT1-ai-review.yaml
GFPT1 gene review (human)
The rate-limiting Fru-6-P + Gln -> GlcN-6-P step (UniProtKB:Q06210, GO:0004360) matches the completed human GFPT1 review.
file:human/GFPT2/GFPT2-ai-review.yaml
GFPT2 gene review (human)
The Fru-6-P + Gln -> GlcN-6-P step (UniProtKB:O94808, GO:0004360) matches the completed human GFPT2 review.
file:human/GNPNAT1/GNPNAT1-ai-review.yaml
GNPNAT1 gene review (human)
The GlcN-6-P -> GlcNAc-6-P acetylation step (UniProtKB:Q96EK6, GO:0004343) matches the completed human GNPNAT1 review.
file:human/PGM3/PGM3-ai-review.yaml
PGM3 gene review (human)
The GlcNAc-6-P <-> GlcNAc-1-P mutase step (UniProtKB:O95394, GO:0004610) matches the completed human PGM3 review.
file:human/UAP1/UAP1-ai-review.yaml
UAP1 gene review (human)
The GlcNAc-1-P + UTP -> UDP-GlcNAc step (UniProtKB:Q16222, GO:0003977) matches the completed human UAP1 review.
file:human/NAGK/NAGK-ai-review.yaml
NAGK gene review (human)
The GlcNAc salvage kinase step (UniProtKB:Q9UJ70, GO:0045127) matches the completed human NAGK review.
6Nodes
5Parts
0Variant Sets
0Variants
5Annotons
4Connections

Derived QC

Recommended-field compliance

100.0% recommended fields populated

All recommended fields populated.

Module deep research

✗ none found

No MODULE:hexosamine_biosynthesis deep-research report alongside the module YAML.

Leaf nodes lacking representative members

✓ every leaf node grounds to a representative protein.

Template conformance

✓ every declared conforms_to bundle matches its template motif.

Reaction chaining (advisory)

✓ every PRECEDES step chains, or its break is acknowledged via chaining_status.

  • gfpt_amidotransfer → glcn6p_acetylation [NOT_CHECKED]
    Glucosamine 6-phosphate links the steps; no CoA carrier is passed on.
  • glcn6p_acetylation → glcnac_mutase [NOT_CHECKED]
    N-acetylglucosamine 6-phosphate links the steps; the free CoA released by the acetyltransferase is a by-product, not an intermediate.
  • glcnac_mutase → udp_glcnac_synthesis [NOT_CHECKED]
    N-acetylglucosamine 1-phosphate links the steps; no CoA carrier is involved.

Function consistency and core coverage

15 gene-function check(s) reflected in core functions · 0 conflict(s) · 2 evidence or coverage gap(s) (20 comparison(s))

Retained noncore functions are reported separately; they do not require promotion to core functions. Support from representative genes does not establish conservation across the whole family. Missing reviews or identifiers leave a claim unverified.

AnnotonParticipantFunctionAssessment
gfpt_activity GFPT1 (human; ubiquitous, rate-limiting)
UniProtKB:Q06210
Family Representative 		L-glutamine:D-fructose-6-phosphate transaminase (isomerizing) activity
GO:0004360 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gfpt_activity GFPT2 (human; tissue-restricted)
UniProtKB:O94808
Family Representative 		L-glutamine:D-fructose-6-phosphate transaminase (isomerizing) activity
GO:0004360 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gfpt_activity GFA1 (Saccharomyces cerevisiae)
UniProtKB:P14742
Family Representative 		L-glutamine:D-fructose-6-phosphate transaminase (isomerizing) activity
GO:0004360 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gfpt_activity gfa1 (Schizosaccharomyces pombe)
UniProtKB:Q09740
Family Representative 		L-glutamine:D-fructose-6-phosphate transaminase (isomerizing) activity
GO:0004360 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gnpnat1_activity GNPNAT1 (human)
UniProtKB:Q96EK6
Family Representative 		glucosamine 6-phosphate N-acetyltransferase activity
GO:0004343 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gnpnat1_activity GNA1 (Saccharomyces cerevisiae)
UniProtKB:P43577
Family Representative 		glucosamine 6-phosphate N-acetyltransferase activity
GO:0004343 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gnpnat1_activity gna1 (Schizosaccharomyces pombe)
UniProtKB:O13738
Family Representative 		glucosamine 6-phosphate N-acetyltransferase activity
GO:0004343 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
pgm3_activity PGM3 (human)
UniProtKB:O95394
Family Representative 		phosphoacetylglucosamine mutase activity
GO:0004610 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
pgm3_activity PCM1/AGM1 (Saccharomyces cerevisiae)
UniProtKB:P38628
Family Representative 		phosphoacetylglucosamine mutase activity
GO:0004610 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
pgm3_activity SPAC13C5.05c (Schizosaccharomyces pombe)
UniProtKB:Q09687
Family Representative 		phosphoacetylglucosamine mutase activity
GO:0004610 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
pgm3_activity SPAC1296.01c (Schizosaccharomyces pombe)
UniProtKB:Q09770
Family Representative 		phosphoacetylglucosamine mutase activity
GO:0004610 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
uap1_activity UAP1 (human)
UniProtKB:Q16222
Family Representative 		UDP-N-acetylglucosamine diphosphorylase activity
GO:0003977 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
uap1_activity QRI1/UAP1 (Saccharomyces cerevisiae)
UniProtKB:P43123
Family Representative 		UDP-N-acetylglucosamine diphosphorylase activity
GO:0003977 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
uap1_activity uap1 (Schizosaccharomyces pombe)
UniProtKB:O94617
Family Representative 		UDP-N-acetylglucosamine diphosphorylase activity
GO:0003977 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
nagk_activity NAGK (human)
UniProtKB:Q9UJ70
Family Representative 		N-acetylglucosamine kinase activity
GO:0045127 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gfpt_activity GFPT / GFAT amidotransferase family
PANTHER:PTHR10937
Family 		L-glutamine:D-fructose-6-phosphate transaminase (isomerizing) activity
GO:0004360 		Family Function Unreviewed
Family review leaves GO:0004360 UNRESOLVED. The complete glutamine-dependent reaction is established for human GFPT1 and GFPT2 by structural and enzyme-kinetic studies (PMID:32019926; PMID:35229715), and thus is not exclusive to the fly-associated SF0. Within that SF0, however, benchmark A8Y5A1 is the native 434-residue Gfat1-PF isoform: the reproducible comparison retains only 40 of 299 glutamine-amidotransferase-domain residues while preserving the sugar-isomerase domains. This contradicts intrinsic execution of the complete two-module reaction by that exact protein, without contradicting the activity of full-length Gfat1. A safe scope therefore depends on both reaction branch and isoform/domain completeness; an unconditional subfamily grant cannot express it.
gnpnat1_activity GNPNAT1 / GNA1 (GNAT) acetyltransferase family
PANTHER:PTHR13355:SF11
Family 		glucosamine 6-phosphate N-acetyltransferase activity
GO:0004343 		Family Supported
Family review supports GO:0004343 for PANTHER:PTHR13355:SF11. SF11 and plant SF19; hexosamine_biosynthesis selects the base family.
pgm3_activity PGM3 / alpha-D-phosphohexomutase family
PANTHER:PTHR45955
Family 		phosphoacetylglucosamine mutase activity
GO:0004610 		Family Supported
Family review supports GO:0004610 FAMILY_WIDE. Asserted by hexosamine_biosynthesis; accepted by every reviewed member.
uap1_activity UAP1 / UDP-N-acetylhexosamine pyrophosphorylase family
PANTHER:PTHR11952
Family 		UDP-N-acetylglucosamine diphosphorylase activity
GO:0003977 		Family Function Unreviewed
Family review leaves GO:0003977 UNRESOLVED. The UAP1 branch has direct enzymatic support and the frog SF4 representative preserves its substrate-pocket architecture. The broad family also includes different UDP-sugar specificities, and the complete set of GlcNAc-active subfamilies is not enumerated. Thus no universal or falsely exhaustive subfamily grant is made.
nagk_activity NAGK / N-acetylglucosamine kinase family
PANTHER:PTHR12862
Family 		N-acetylglucosamine kinase activity
GO:0045127 		Family Supported
Family review supports GO:0045127 FAMILY_WIDE. Asserted by hexosamine_biosynthesis; accepted by human NAGK.

Gene-review completeness (15/15 grounded genes reviewed)

14 complete review(s) · 4 with deep research · 0 missing review · 11 reviewed but lacking deep research

Gene Review Complete Deep research
GFA1 P14742 ✓ ✓ ✓
GFPT1 Q06210 ✓ 29/30 ✗
GFPT2 O94808 ✓ ✓ ✗
gna1 O13738 ✓ ✓ ✗
GNA1 P43577 ✓ ✓ ✓
GNPNAT1 Q96EK6 ✓ ✓ ✗
NAGK Q9UJ70 ✓ ✓ ✗
PCM1 P38628 ✓ ✓ ✓
PGM3 O95394 ✓ ✓ ✗
QRI1 P43123 ✓ ✓ ✓
SPAC1296.01c Q09770 ✓ ✓ ✗
SPAC13C5.05c Q09687 ✓ ✓ ✗
SPBC12C2.11 Q09740 ✓ ✓ ✗
uap1 O94617 ✓ ✓ ✗
UAP1 Q16222 ✓ ✓ ✗

Details

Context
eukaryotesNCBITaxon:2759
cytosolGO:0005829
Eukaryotic hexosamine biosynthesis and GlcNAc salvageMetabolic Pathwayhexosamine_biosynthesis
UDP-N-acetylglucosamine biosynthetic processGO:0006048
Context
eukaryotesNCBITaxon:2759
cytosolGO:0005829

ALIGN (YeastPathways project, 2026-10): the human-grounded module was kept at eukaryotic scope and gained S. cerevisiae (GFA1 P14742, GNA1 P43577, PCM1 P38628, QRI1 P43123) and S. pombe (gfa1 Q09740, gna1 O13738, the two phosphoacetylglucosamine mutase paralogs SPAC13C5.05c Q09687 and SPAC1296.01c Q09770, uap1 O94617) exemplars; every yeast protein falls in the same PANTHER family as the human representative (PTHR10937, PTHR13355, PTHR45955, PTHR11952). YeastCyc gene assignments for UDPNAGSYN-YEAST-PWY are correct and complete for the four de novo steps. The NAGK salvage branch is now marked optional because neither the SGD nor the PomBase model contains a GlcNAc kinase; S. cerevisiae cannot use exogenous GlcNAc. GO-CAM agreement: both yeast models place all four activities in cytosol with the same MF terms used here; the PomBase model additionally includes pgi1 (glucose-6-phosphate isomerase, glycolysis) upstream, which is outside this module. Connections were converted to PRECEDES for the de novo chain. UDP-GlcNAc is the amino-sugar donor for the n_glycan_llo_assembly_cytoplasmic module (ALG7/DPAGT1 and ALG13/ALG14), chitin synthesis, GPI anchors and, in animals, O-GlcNAcylation and sialic-acid synthesis. Bacteria use a different order (GlmS, GlmM mutase on glucosamine 6-phosphate, then bifunctional GlmU acetyltransferase/uridylyltransferase), which is a separate pathway realization, not a variant of this eukaryotic chain. Notable moonlighting captured in the human gene reviews (kept non-core here): UAP1 protein-serine pyrophosphorylase (IRF3, type-I-IFN) and NAGK muramyl-dipeptide kinase (NOD2). Disorders: GFPT1 CMS12, GNPNAT1 rhizomelic skeletal dysplasia, PGM3-CDG.

Connections

The GlcN-6-P made by GFAT is N-acetylated by GNA1/GNPNAT1.
The GlcNAc-6-P made by GNA1/GNPNAT1 is converted to GlcNAc-1-P by PCM1/PGM3.
The GlcNAc-1-P made by PCM1/PGM3 is the substrate for QRI1/UAP1.
glcnac_salvage -> glcnac_mutase Provides Input For
NAGK feeds salvaged GlcNAc-6-P into the pathway at the mutase step (the same node GNA1/GNPNAT1 produces), recycling free GlcNAc from glycoconjugate degradation into UDP-GlcNAc.
Part 1: amidotransfer (rate-limiting; Fru-6-P + Gln)
Glutamine:fructose-6-phosphate amidotransferase (GFAT)Reactiongfpt_amidotransfer

Annotons

GFAT: glutamine-fructose-6-phosphate transaminase (isomerizing)
gfpt_activity
Participant: Family: GFPT / GFAT amidotransferase family
Family:
GFPT / GFAT amidotransferase familyPANTHER:PTHR10937
Representative Members: GFPT1 (human; ubiquitous, rate-limiting)UniProtKB:Q06210 GFPT2 (human; tissue-restricted)UniProtKB:O94808 GFA1 (Saccharomyces cerevisiae)UniProtKB:P14742 gfa1 (Schizosaccharomyces pombe)UniProtKB:Q09740

Function

L-glutamine:D-fructose-6-phosphate transaminase (isomerizing) activityGO:0004360
Substrates: D-fructose 6-phosphate L-glutamine
Products: D-glucosamine 6-phosphate L-glutamate

Locations

cytosolGO:0005829

Aminate Fru-6-P with glutamine to GlcN-6-P (rate-limiting HBP step).

Part 2: N-acetylation (acetyl-CoA)
Glucosamine-6-phosphate N-acetyltransferase (GNA1/GNPNAT1)Reactionglcn6p_acetylation

Annotons

GNA1/GNPNAT1: glucosamine-6-phosphate N-acetyltransferase
gnpnat1_activity
Participant: Family: GNPNAT1 / GNA1 (GNAT) acetyltransferase family
Family:
GNPNAT1 / GNA1 (GNAT) acetyltransferase family
Representative Members: GNPNAT1 (human)UniProtKB:Q96EK6 GNA1 (Saccharomyces cerevisiae)UniProtKB:P43577 gna1 (Schizosaccharomyces pombe)UniProtKB:O13738

Function

glucosamine 6-phosphate N-acetyltransferase activityGO:0004343
Substrates: D-glucosamine 6-phosphate acetyl-CoA
Products: N-acetyl-D-glucosamine 6-phosphate coenzyme A

Locations

cytosolGO:0005829

N-acetylate GlcN-6-P to GlcNAc-6-P (acetyl-CoA).

Part 3: phosphohexomutase (6-P <-> 1-P)
Phosphoacetylglucosamine mutase (PCM1/AGM1/PGM3)Reactionglcnac_mutase

Annotons

PCM1/PGM3: phosphoacetylglucosamine mutase
pgm3_activity
Participant: Family: PGM3 / alpha-D-phosphohexomutase family
Family:
PGM3 / alpha-D-phosphohexomutase familyPANTHER:PTHR45955
Representative Members: PGM3 (human)UniProtKB:O95394 PCM1/AGM1 (Saccharomyces cerevisiae)UniProtKB:P38628 SPAC13C5.05c (Schizosaccharomyces pombe)UniProtKB:Q09687 SPAC1296.01c (Schizosaccharomyces pombe)UniProtKB:Q09770

Function

phosphoacetylglucosamine mutase activityGO:0004610
Substrates: N-acetyl-D-glucosamine 6-phosphate
Products: N-acetyl-D-glucosamine 1-phosphate

Locations

cytosolGO:0005829

Interconvert GlcNAc-6-P and GlcNAc-1-P (Mg2+).

Part 4: uridylyltransfer (UTP -> UDP-GlcNAc)
UDP-N-acetylglucosamine pyrophosphorylase (QRI1/UAP1)Reactionudp_glcnac_synthesis

Annotons

QRI1/UAP1: UDP-N-acetylglucosamine pyrophosphorylase
uap1_activity
Participant: Family: UAP1 / UDP-N-acetylhexosamine pyrophosphorylase family
Family:
UAP1 / UDP-N-acetylhexosamine pyrophosphorylase familyPANTHER:PTHR11952
Representative Members: UAP1 (human)UniProtKB:Q16222 QRI1/UAP1 (Saccharomyces cerevisiae)UniProtKB:P43123 uap1 (Schizosaccharomyces pombe)UniProtKB:O94617

Function

UDP-N-acetylglucosamine diphosphorylase activityGO:0003977
Substrates: N-acetyl-D-glucosamine 1-phosphate UTP
Products: UDP-N-acetyl-D-glucosamine (UDP-GlcNAc) diphosphate

Locations

cytosolGO:0005829

Condense GlcNAc-1-P + UTP to UDP-GlcNAc (final step).

Part 5: GlcNAc salvage (recycling; lineage-dependent) (optional)

Present in animals (NAGK). No GlcNAc kinase is assigned in the S. cerevisiae (YeastPathways) or S. pombe (PomBase) models, so the salvage entry point is not a required part of the eukaryotic module.

N-acetylglucosamine kinase (NAGK)Reactionglcnac_salvage

Annotons

NAGK: N-acetylglucosamine kinase
nagk_activity
Participant: Family: NAGK / N-acetylglucosamine kinase family
Family:
NAGK / N-acetylglucosamine kinase familyPANTHER:PTHR12862
Representative Members: NAGK (human)UniProtKB:Q9UJ70

Function

N-acetylglucosamine kinase activityGO:0045127
Substrates: N-acetyl-D-glucosamine (free; from glycoconjugate turnover) ATP
Products: N-acetyl-D-glucosamine 6-phosphate ADP

Phosphorylate free GlcNAc to GlcNAc-6-P (salvage into the HBP).